Ozone is a very strong oxidant and is used in various fields such as for disinfection, sterilization, discoloration, deodorization, oxidative decomposition, oxidative treatment, and so on. Since ozone can be readily decomposed into oxygen spontaneously, the treatment method of utilizing ozone can be a method with non cross contamination. Ozone-water, wherein ozone is dissolved, is safer and easier to be handled as compared to ozone gas. When ozone coexists with moisture or is dissolved in water, the oxidizing ability of ozone is further improved, and generally used for disinfection, cleaning, and so on (see, for example, Non-patent Document 1). For these purposes, developing a method for producing ozone-water, which can more easily, more conveniently, and more efficiently produce ozone-water, has been in demand.
For a method to produce gaseous ozone, a UV lamp method, a silent discharge method, and an electrolysis method are known (see, for example, Non-patent Document 2). The UV lamp method, wherein a small amount of ozone is produced, is usually used for removing a small amount of odor, such as for deodorizing a room or a car. The silent discharge method is a general method for producing ozone gas. However, when atmospheric air is used as the ingredient, nitrogen oxide is simultaneously produced. In order to prevent this, oxygen gas should be used as the ingredient, or an attachment device, which concentrates only oxygen contained in atmospheric air, should be equipped. Moreover, impurity incorporation also becomes a problem wherein metal impurity gets mixed in ozone gas due to a metal electrode being worn away. In contrast, ozone gas can be obtained by water electrolysis. According to the electrolysis method, ozone gas with high purity and high concentration can be easily obtained, even though the obtained ozone gas contains moisture to some extent.
For a method to obtain ozone-water, some methods are known wherein ozone gas, obtained by the above-described methods, is dissolved in water, or wherein ozone-water is produced directly by the electrolysis method. Ozone-water could be obtained by running ozone gas, produced according to the silent discharge method or the electrolysis method, through a vapor-liquid dissolution tower and dissolving the ozone gas in water. However, this kind of method would make a device larger and more complicated. On the other hand, according to the electrolysis method, wherein an electrolysis cell is constituted with a porous or a mesh anode and a porous or a mesh cathode interposing a solid polymer film therebetween and the electrolysis cell is used so as to electrolyze tap water or purified water, ozone-water can be directly produced. Moreover, a device for this kind of method can be easily made into a small size.
The materials used for an electrode for producing ozone-water by the electrolysis method, are generally platinum, gold, platinum-coated titanium, lead oxide, and so on, because of their prominent catalytic functions. These materials are formed into a porous or a mesh structure to be used as an anode 3. The anode 3 and a suitable cathode 5 interpose a solid polymer film 7 therebetween, which, as a result, constitute an electrolysis cell 1, shown, for example, in FIG. 12. Ozone-water can be obtained by water electrolysis while supplying purified water or tap water in an anode chamber 13 of the electrolysis cell 1. In case of producing ozone-water by the electrolysis method as described above, producing ozone-water of an intermediate to high temperature by using warm water at, for example, 42° C. as ingredient water is proposed (see, for example, Patent Document 1). The obtained ozone-water can be used through a shower and the like for disinfecting an entire body.
However, in a case, such as in Patent Document 1, wherein platinum is used as the electrode, a problem has been pointed out in which the electrode gets worn away and dissolved as the electrode is used in electrolysis for producing ozone-water. Even with a platinum electrode, which is considered to have a relatively better durability, or even with the electrode described above, the phenomenon wherein the metal constituting the anode is dissolved as ions is caused, as the electrode is used under the condition for producing ozone in which a large electric current and a large voltage are applied. Since the dissolved metal ions adhere to the solid polymer film and disturb the reaction, the efficiency in ozone production gradually decreases. The inventors of the present invention conducted a comparative test in which warm ozone-water was produced by using a platinum electrode. The result shows that platinum was severely worn away particularly when ozone production was continuously performed in a high-temperature range. Therefore, even by using the above-described apparatus, obtaining warm ozone-water continuously in a long term is considered difficult.
In order to reduce the wearying caused by electrolysis as much as possible, ozone-water of an intermediate to high temperature can be produced in such a way that low-temperature water whose temperature is in the range up to 10° C. is supplied so as to produce ozone-water of a low temperature, and the produced ozone-water is heated so as to be, for example, 25-70° C. However, as known that the solubility of gas decreases as water temperature becomes higher, there is a risk in that ozone gas dissolved in water at a low temperature becomes excessive when water is heated to an intermediate to high temperature, and is released as ozone gas. In a case wherein ozone-water is heated after being produced, the efficiency in producing ozone-water is low, since some of the produced ozone is to be wasted by such release. Therefore, in order to efficiently produce ozone-water of an intermediate to high temperature, the temperature of water to be supplied is preferably maintained in an intermediate to high temperature range when the water is fed to an electrolysis cell.
Recently, a diamond film with electric conductivity is suggested as a material for an electrode in places of platinum and the like. The principal characteristics of the conductive diamond film include unique characteristics which cannot be seen in other materials for an electrode: for example, the conductive diamond film has high mechanical strength and high chemical inertness; molecules are not easily adsorbed to the diamond film; the diamond film exhibits a wide potential window in which oxidative decomposition and reductive decomposition of solvent do not easily occur; there is selectivity of the reaction, and so on. Therefore, producing ozone by using a diamond film has been considered (see, for example, Patent Document 2). In such apparatus, the diamond film is formed on a mesh or a porous substrate by a Hot Filament Chemical Vapor Deposition (CVD) or a microwave plasma assisted CVD, and such substrate having the diamond film formed thereon is used as an anode in an electrolysis cell formed in a configuration wherein a solid polymer film is interposed by electrodes.    Non-Patent Document 1: (February 1993). New Edition of New Technology for Utilizing Ozone: Sanyu Shobo    Non-Patent Document 2: Sugimitsu, Hidetoshi (February 1996). Basics and Applications of Ozone: Korin    Patent Document 1: Unexamined Japanese Patent Publication No. 2004-60011    Patent Document 2: Unexamined Japanese Patent Publication No. 9-268395